A conventional type of a motor for use in controlling an air control door such as an air mixing door constituting one of the component elements of a vehicle air conditioning device is controlled in such a way that both an output signal V.sub.M produced at a position sensor for use in sensing an operational position of said air mixing door and another output signal V.sub.1 produced by amplifying an output signal V.sub.D produced at a setting means for use in setting a position of said air mixing door are differentially amplified by a differential amplifier, and then their calculated output V.sub.IN is applied.
However, the conventional type of vehicle motor driving circuit disadvantageously exhibits a poor response characteristic because an integrator circuit for use in removing noise is additionally arranged at a calculating amplifier for amplifying an output signal V.sub.D produced at a position setting means for use in setting a position of said air mixing door, and further a period of time T is required until the output signal V.sub.1 is increased up to a desired value because output signal V.sub.1 shows a specific signal in which it may gradually be increased from a time T.sub.o when a power supply switch is turned on as shown in FIG. 1(b). On one hand, the signal V.sub.M produced at the air mixing door position sensor shows a desired value at once at a time T.sub.o when the power supply switch is turned on (FIG. 1(a)), so that said signal V.sub.M becomes higher than said signal V.sub.1 immediately after the time T.sub.o when the power supply switch is turned on. As a result, the motor is erroneously operated just after the time T.sub.o when the power supply switch is turned on to cause the air mixing door to be slightly rotated in its cooling mode in which a volume of cold air is increased or a heating mode in which a volume of warm air is increased. Then, it is required to vary a setting position of the air mixing door up to such a position as indicated by the position setting means after the period of time T is passed. That is, this conventional type of door undesirably produces an unpleasant chattering sound at the gear trains cooperatively connected to the motor just after the power supply switch is turned on because the motor is rotated for a short period of time irrespective of any operational positions set in the position setting means and the position sensor. Further, the conventional type of vehicle motor driving circuit undesirably when the position setting means is abruptly changed, for example, from its full cooling mode to its full heating mode or when turned from its full heating mode to its full cooling mode, the locked condition of the motor may be kept as an operation of the motor locking inhibitor circuit constituted by a capacitor for sensing a load of the motor is not released, resulting in that a position of the air mixing door may not be controlled in response to a signal from the position setting means.